A long-standing problem in the testing of characteristics of thermo-plastic materials has related to the recovery of a sample which has been mixed under conditions intended to simulate those encountered during production. In such testing, it is of course desired that the sample not be materially altered or affected during the process of its removal from the test chamber.
In the past, test apparatus for thermoplastic material have not been adapted to ease of removability of the sample, or to ease of reproduceability of such samples. Accordingly, efforts in securing adequate quality control over various extrusion and other plastic-forming processes have been encumbered by the tendency of the plastic materials to resist removal from such prior art test chambers.
More particularly, a typical prior art mixer would consist of a mixing chamber in which counter-rotating rotors impact against granules of the test material, thus involving pressure against the walls of the mixing chamber and within the test material. Such mixers are usually thermal-liquid heated and consist of a bowl and backstand. The backstand is generally equipped with a plurality of gears which serve to drive the rotors as well as to regulate their rate of rotation.
After the test material is introduced into the mixer bowl, it is heated and mixed until fluxing occurs, this will produce various shear processes which are a result of the physical and chemical effects of the conditions of heat and pressure occurring by virtue of the mixing.
The measuring objective of such testing is to monitor the time span during which the material possesses its lowest viscocity, that is, the period prior to cross-linking. This time span is of significance in the optimization of process-conditions during extrusion, injection molding, lamination and other procedures.
The construction of commonly available mixers requires that the rotors rotate sufficiently long until the cross-linking or setting of the thermoplastic material occurs; however, in this approach, the rotating force of the rotors will often mechanically impair or destroy the sample, often reducing it to powder form. Thus, all that is often left to test, is a pulverized sample. Further, even where such pulverization does not normally occur, the full or partial impairment of the thermo-set physical structure of the sample is often unavoidable in order to effectuate its removal from the mixer bowl and to permit essential cleaning of the bowl, rotors and backstand so that the apparatus can be reused for future tests.
On occasion, the material may cure or harden within the bowl to such an extent that its removal is impossible without forcibly hammering or chiseling the sample out. Obviously, such an approach not only impairs the physical characteristics of the sample, but also can cause substantial harm to the test apparatus which may be formed of stainless steel and/or other material sensitive to abrasion and injury. Accordingly, it may be appreciated that such a procedure for obtaining thermoplastic samples has become a major drawback in the perfection of various plastic-forming processes.
It is to be further noted that the instant problem has related not only to thermosetting problems in plastics, but also to those involving other materials such as fiberglass, clays, asbestos, quartz-base materials, and wood-related materials. Such materials often have strong abrasive properties and have presented problems in the damaging of test apparatus.
Hence, it is to be appreciated that a problem has long existed with respect to test reproduceability and correlation of material samples.
Thusly, the present inventive method may be viewed as a solution to this long-standing problem.